Grain-oriented electrical steel sheet is steel sheet usually containing Si up to 7% and having a secondary recrystallized texture of secondary recrystallized grains aligned in the {110}<001> orientation (Goss orientation). The magnetic properties of grain-oriented electrical steel sheet basically are greatly affected by the {110}<001> alignment of the secondary recrystallized grains. For this reason, up to now, there has been much R&D conducted into methods of production for improving the alignment of secondary recrystallized grains (for example, see U.S. Pat. No. 3,287,183 and Japanese Patent Publication (B2) No. 62-45285).
However, as explained in “IEEE Transactions on Magnetics” MAG-14 (1978), pp. 350-352, it is learned that if the orientation alignment becomes too high, conversely the core loss characteristic deteriorates. Therefore, for example, the deviation angle (α) around the rolling surface normal direction (ND) from the {110}<001> ideal orientation, the deviation angle (β) around the traverse direction (TD), and the deviation angle (γ) around the rolling direction (RD) are being used to further refine the orientation alignment and study the relationship with the core loss characteristic.
Here, FIG. 1 shows the definitions of the deviation angles on a {100} pole figure (see “IEEE Transactions on Magnetics” MAG-14 (1978), pp. 252-257). Further, FIG. 2 schematically shows the ideal {110}<001> oriented grains. Further, FIG. 3(a) schematically shows the secondary recrystallization orientation and deviation angles (α and β), while FIG. 3(b) schematically shows the secondary recrystallization orientation and the deviation angle (γ).
Further, in the above studies, as measures for improving the core loss characteristic, several grain-oriented electrical steel sheets defining the alignment of secondary recrystallized grains based on the above deviation angle indicators have been proposed.
For example, Japanese Patent Publication (B2) No. 57-9418 discloses grain-oriented electrical steel sheet superior in magnetic properties having a crystal structure comprised of {h,k,0} planes with <001> axes of the individual crystal grains matching with the rolling direction of the steel sheet and with indexes of the crystal planes parallel to the steel sheet surface dispersed rotated around the rolling direction.
However, the <001> axes of crystal grains of actual products, as shown in FIG. 3(a), are also dispersed around the ND and/or TD, so making the <001> axes of the individual crystal grains match in the rolling direction of the steel sheet is difficult.
Further, Japanese Patent Publication (A) No. 59-177349 and “IEEE Transactions on Magnetics” MAG-14 (1978), pp. 252-257 disclose low core loss grain-oriented electrical steel sheet comprised of a crystal structure with [001] axes of the secondary recrystallized grains inclined with respect to the rolling surface by 4° or less, preferably 2° or so.
However, while this grain-oriented electrical steel sheet has the <001> axes of the individual crystal grains inclined around the traverse direction (TD), the deviation angle (α) around the rolling surface normal direction (ND) and the deviation angle (γ) around the rolling direction (RD) are not prescribed.
In this way, several discoveries have been obtained regarding the relationship between the deviation angles from the {110}<001> ideal orientation and the core loss characteristic for a simple system such as described in Japanese Patent Publication (B2) No. 57-9418 or Japanese Patent Publication (A) No. 59-177349, but the relationship between the actual orientation distribution about {110}<001> and the core loss characteristic has not been grasped overall.